4-Hydroxy-2-pyrrolidone is used as an intermediate for medicines, agricultural chemicals, etc. The following processes for preparing it are known. These are a process for preparing it from a 4-chloro-3-hydroxybutyrate and ammonia Japanese Patent Publication No. 183756/1982, Tetrahedron Lett., 41,5603(1985), Japanese Patent Publication No. 176564/1986!, a process for preparing it from a 4-chloro-3-hydroxybutyrate and benzylamine (Japanese Patent Publication No. 45360/1989), a process for preparing it from a cyclobutanone derivative and optically active .alpha.-methylbenzylamine (Synthetic Comm., 21,693(1991), a process for preparing it from 3,4-epoxibutyramide and optically active .alpha.-methylbenzylamine (J. Chem. Research(s), 376, 1990), a process for preparing it by heating and dehydrating 4-amino-3-hydroxybutyric acid (abbreviated to GABOB hereinafter) Tetrahedron Lett., 21,2443(1980), J. Org. Chem., 19,1-589(1954)!, a process for preparing it from optically active GABOB and hexamethyldisilazane (Synthesis, 1978, 614), a process for preparing it from optically active 4-hydroxyproline (Japanese Patent Publication No. 250352/1988) and a process for preparing it from a 4-bromo crotonic acid ester J. Org. Chem., 44,2798(1979)!.
These processes, however, have following disadvantages industrially: The process from a 4-chloro-3-hydroxybutyrate and ammonia produces many kinds of by-products and it is difficult to achieve high yield. The process from benzylamine or .alpha.-methylbenzylamine needs debenzylation or demethybenzyllation procedure after constructing a pyrrolidone skeleton and this procedure is so troublesome as it uses an alkali metal in liquid ammonia at low temperature. The process by heating and dehydrating GABOB is low in the yield and in case using an optically active compound, the racemization occurs. The process from optically active GABOB and hexamethyldisilazane is high in the yield, but the hexamethyldisilazane is expensive and the process needs desilylation procedure after constructing pyrrolidone skeleton. The process from optically active 4-hydroxyproline or a 4-bromo crotonic acid ester comprises many steps, and it is not practical. Therefore, a more efficient process for preparing 4-hydroxy-2-pyrrolidone was desired.